Brazilian President Luiz Inacio Lula da Silva's commanding lead over opposition candidate Geraldo Alckmin narrowed slightly and the October election could go to a runoff vote, a poll showed on Tuesday.

Brazilian President Luiz Inacio Lula da Silva speaks with his US counterpart George W. Bush (not pictured) during a bilateral meeting on the sidelines of the G8 summit outside Saint Petersburg. World Trade Organisation heavyweights set yet another timetable which they hope will salvage the floundering Doha Round negotiations on tearing down barriers to commerce. [AFP]

Lula would win 44 percent of the votes compared with Alckmin's 28 percent in a first-round vote, according to a poll by survey group Datafolha broadcast on Globo TV.

The poll said Lula might need to wait until a second-round vote to win a second term. His dip in the poll was within the 2 percentage points margin of error.

Earlier polls had shown Lula with the absolute majority needed to win the election outright in the first round and avoid a runoff.

Lula slipped as Sen. Heloisa Helena, a firebrand from a small leftist party, rose to 10 percent from 6 percent in the poll. Three lesser known candidates each received 1 percent in the poll.

In June, the Datafolha poll showed Lula will 46 percent and Alckmin with 29 percent in the first round. In May, Lula had 45 percent and his main rival 22 percent.

The latest survey polled 6,264 people in 272 municipalities on Monday and Tuesday.

The popularity of Lula, Brazil's first working-class president, has rebounded from a corruption scandal last year that involved several high-ranking members of his left-leaning Workers' Party. He has also been helped by a rise in the minimum wage and an improving economy.

Alckmin is expected to be helped by television advertising by his centrist Brazilian Social Democracy Party (PSDB) and the allied Liberal Front Party during June.

Alckmin will have about 30 percent more free air time than Lula when televised campaign advertisements start on August 15.

The PSDB camp is hoping this advantage will help boost the name recognition of Alckmin, who is still relatively unknown outside of his home state, Sao Paulo.